All Eukaryotes are protists except plants, animals and fungi mostly unicellular amoeba, slime molds, algae, protozoa Extraordinarily diverse typically larger than prokaryotes functions carried out by organelles membrane bound nucleus First undisputed fossils ~1.8 bya spherical algal protists many protists no hard parts common ancestry unresolved
Origin of the nuclear membrane? Origin of mitochondria (organelle that produces energy)? All eukaryotic cells have mitochondria so mitochondria are homologous… Origin of chloroplasts? Photosynthetic eukaryotes have chloroplasts some from common ancestor others….?
Origin of the nuclear membrane? Origin of mitochondria (organelle that produces energy)? All eukaryotic cells have mitochondria so mitochondria are homologous… Origin of chloroplasts? Photosynthetic eukaryotes have chloroplasts some from common ancestor others….? Endosymbiosis: Organisms of one species living inside an organism of another species proposed in 1905 but way too crazy
Mitochondria and chloroplasts are about the size of an average bacterium Both organelles replicate independently by fission, as do bacteria have their own ribosomes to make their own proteins mitochondria/chloroplasts each have a circular chromosome Both organelles have double membranes consistent with the engulfing mechanism Genes of each organelle closely resemble ancestors! cyanobacteria for chloroplasts proteobacteria for mitrochondria some genes appeared to have shifted from bacteria to host, possibly explaining why ‘mitochondria’ are not free-living
Algae ingested by other heterotrophic eukaryotes! led to Euglenoids, Diatoms and Brown algae Chloroplasts transferred to other protists results in chloroplasts not from common ancestor! How do we know this happened? HINT: # of membranes around organelles = ____
Haplonic life cycles: most life spent with one set of chromosomes (1N) all cells are haploid (some multi-cellular algae, and fungi) zygote only diploid cell → meiosis into daughter cells Diplonic life cycles: most life with pairs of chromosomes (2N) body cells (e.g., animals) are all diploid sex cells (gametes) are haploid via meiosis → then fuse Asexual life cycles: binary fission nucleus divides, then cell divides into two separate organisms → mitosis many-single celled protists can switch to asexual reproduction There are more…. parasites require hosts
More complex life cycles include an alternation of generations some algae and plants both generations must be multi-cellular AOG = the alternation of multi-cellular haploid and diploid generations diploid (2N) = sporophyte → makes spores haploid (1N) = gametophyte → male/female → make gametes fertilization of gametes makes new sporophyte In some species the different generations look similar while in others they look different